The depression is one type of mood disorders, and its predominant symptoms are the “depressed mood” and “loss of interest or pleasure”, but some patients complain other symptoms such as suppressed appetite, insomnia, fatigue, suicidal ideation etc. Its diagnosis is generally conducted based on the criterion under either ICD-10 (International Classification of Diseases) by WHO (World Health Organization) or “DSM-IV” by American Psychiatric Association.
However, the diagnosis of depression can be hardly objective because it depends on the impression by physician or psychologists, or impression by the patients or individuals complaining the symptom or stress. In fact, cases are often observed where symptoms are excessively reported either intentionally or unintentionally because of the disease gain in which a patient is somehow benefitted from the state of being sick, or otherwise symptoms are concealed for the purpose of avoiding prejudice or trouble from being known to be in depression. In such cases, accurate diagnosis of the disease is difficult, and determination of treatment method may become difficult, or even inappropriate treatment might be applied due to misdiagnosis.
Therefore, several methods have been tested to objectively assist the diagnosis by physician or psychologists. One example is the method in which the noise appearing in the symptom of a patient is excluded as much as possible by processing the results of diagnosis made by a physician or psychologist with a computer (WO2004/080312).
Several markers for depression are known, including macromolecular materials which have been reported in the method to measure the expression level of a gene (JP2008-253258) and the method to detect proteolytic products (JP2009-92550).
On the other hand, smaller compounds in living bodies are also tested as candidates for the depression marker, including those having been reported in the method to measure and analyze the contents of testosterone and cortisol (JP2007-24822) and the method to detect the degraded products of tryptophan in vivo (WO2006/105907), but none of them is brought into practice use so far.